Technical Abstract:
Management of lepidopteran pests of crucifers is problematic due to increasing incidence of insecticide resistance and potential restrictions on insecticide use. In this study we evaluated season-long microbial control of 3 pests of fresh-market cabbage: the diamondback moth (DBM), the imported cabbageworm (ICW), and the cabbage looper (CL). The use of Beauveria bassiana (Bb) alone, at either of 3 rates, reduced DBM numbers. At higher rates, Bb application resulted in reduced numbers of ICW and CL. Bacillus thuringiensis applications at either of 2 rates resulted in reduced counts of all three pests. Four applications of Bb followed by 2 late-season applications of Bt reduced larval counts of all 3 pests. Combined applications of Bb and Bt were no better at reducing larval counts than Bt alone at either rate. Laboratory efficacy of Bb-treated leaves for DBM averaged approximately 80% for freshly-treated leaves but dropped to approximately 40% for samples taken 3 d after spray. There were no differences among average cabbage head weights from treated and untreated plots. Cabbage head marketability was best among Bt-treated plots and reduced among heads from plots treated with Bb. In conclusion, Bb worked well alone against DBM and provided some control of the other pests. Combining early season Bb with later applications of Bt or chemical insecticides may also help to slow or limit the development of resistance.